The present invention relates generally to the field of sight glasses and retaining structures for such devices. More particularly, the invention relates to a novel sight glass retaining system which facilitates installation and effective retention of a sight glass in a cost-effective assembly.
A number of applications exist for sight glasses and similar structures. In general, sight glasses permit viewing of an article or process through a barrier or panel which would otherwise occlude vision. By way of example, in combustion chambers, furnaces, water heaters, and the like, pilot flames and combustion may take place in a closed combustion chamber. A combustion chamber may, in fact, be sealed, or may be simply shielded by surrounding panels. The panels may typically be made of a combustion-resistant material, such as sheet metal, and may include insulation layers on one or both sides. In general, however, such panels or barriers preclude visual assessment of processes occurring within the enclosed chamber. Such visual assessment is often useful to determine whether the processes are proceeding normally, or whether servicing or other action is necessary. In furnaces and water heating applications, for example, it may be useful to assess whether pilot flames are lit or active, electric heating elements are activated, combustion is ongoing, and so forth.
Various arrangements have been proposed and are presently in use for providing sight glasses in such applications. In certain conventional arrangements, for example, sight glasses are retained by screw-on clips, tack-welded assemblies, and so forth. While such retaining systems generally provide for adequate mounting and retention of sight glasses, they are not without drawbacks. For example, manufacturing processes for forming and mounting such arrangements may be somewhat costly and time-consuming. Where tack-welded arrangements are employed, special processing of the components, including the retainer and panel may be required. Moreover, such arrangements may limit or even make impossible the ability to seal the sight glass either within the retainer, against the panel, or both. Finally, conventional arrangements may limit or even make impossible the eventual servicing or replacement of the sight glass or retainer.
There is a need, therefore, for an improved technique for retaining sight glasses and similar structures. There is a particular need for a straightforward and cost-effective structure which effectively mounts a sight glass or similar component in various applications such as those discussed above.
The present invention provides a sight glass retention system designed to respond to such needs. The technique may be employed in a wide variety of settings, and is generally applicable to any setting in which a planar or curved sight glass or similar panel is to be held and retained on a mounting or support surface. In a present configuration, the system is adapted for mounting a sight glass on a support panel, such as might be found in a furnace, water heater, process equipment, and the like. The technique makes use of a retainer that forms a frame behind which the sight glass is positioned. Retaining tabs are formed on peripheral flanges around the frame and are designed to interface with mating features of the support panel. In one embodiment, for example, resilient retaining portions are formed in the retaining tabs that clip into place once the assembly is mounted on the support panel. The retaining portions contact a rear surface of the support panel to maintain the retainer and sight glass in position, such as adjacent to an aperture through which a process can be viewed. One or more seals or gaskets may be provided in the assembly. A sealing element, for example, may be applied directly to or around the sight glass and compressed against the inner surface of the retainer or against the outer surface of the support panel, or both, to provide sealing engagement at those locations. The sealing element may be sufficiently resilient to undergo elastic compression during mounting, thereby forcing tight engagement of the retainer, sight glass and retaining tabs following installation.
The technique also provides for forming and configuring the retaining system, particularly the retainer itself. The retainer may be made of any suitable material, such as metal. In an exemplary process for making the retainer, a blank is stamped from sheet metal and peripheral flanges surrounding the frame portion of the retainer are bent in a progressive dye or other tooling. The retaining portions formed on the retaining tabs may be sheered and bent during this process so as to force them to extend in a direction from the retaining tabs as desired to contact the support panel when the assembly is clipped into place. The flanges formed around the frame portion of the retainer by the bending operation serve to locate and retain the sight glass in the assembly. The sight glass may then be mounted into the retainer and the sealing element placed either on the support panel or on the sight glass or frame. In exemplary implementation, a bead of resilient material is applied directly to the sight glass which can then be dropped into the retainer and the entire assembly is snapped into place on the support panel.